This invention relates to steam showers and more particularly to a steam shower having an improved construction that facilitates maintenance.
Steam showers are widely used on paper machines to improve the operation of the machines as well as to improve the moisture profile of the paper products produced thereby. When steam contacts the cold surface of a moving paper web, it condenses into water. During the condensation, latent heat is released from the steam and absorbed by the moving web. With the absorption of the latent heat, the temperature of the moving web increases and therefore the tension inside the moving web decreases. Reduction of the tension inside the web allows the paper machine to run at a higher speed without breaking the web. Higher machine speed directly results in increased production. Another effect of higher web temperature is a reduction in the viscosity of water trapped among the fibers of the web. It is easier for the pressing nips located at the press section of the paper machine to remove moisture with lower viscosity from the web. In other words, it is easier for the pressing nips to remove hotter water from the web. Therefore, steam showers are normally installed right in front of the pressing nips for moisture profiling purpose.
A profiling steam shower generally includes a cross-beam structure, an array of steam valves and corresponding steam diffusers. The purposes of the cross-beam structure of the steam shower are twofold: it supports the structure of the steam shower across the whole width of paper machine and it also distributes process steam along the cross-machine (CD) direction inside the cross-beam. The steam valves located at each and every segment (or zone) of the cross-beam receive the process steam from the cross-beam structure and deliver the correct amount of process steam to each corresponding steam diffuser according to control signals sent from a control system. The steam diffuser further distributes the process steam to the surface of the moving web uniformly across the whole CD length of the steam diffuser.
A traditional steam shower has a highly integrated construction that requires the steam shower to be completely removed from the paper machine in order to perform service on steam actuator valve modules or steam diffusers. Some steam showers, however, do have a construction that permits the steam diffusers to be accessed for cleaning without the removal of the entire steam shower. One such steam shower is shown in U.S. Pat. No. 6,408,534 to Alen et al. The steam shower or steam box disclosed in the Alen et al. '534 patent includes a plurality of steam diffusers or regulator chambers covered by one or more hinged perforated screens, which may be pivoted upward to provide access to the regulator chambers. Since space must be provided to permit the perforated screens to be pivoted outward and upward, the steam shower of the Alen et al. '534 patent may not desirable for some applications.
Another steam shower that provides access to steam diffusers is shown in U.S. Patent Application Publication No. 2006/0107704 to Passiniemi. The steam shower in the Passiniemi publication has a plurality of steam diffusers or steam discharge chambers covered by a fixed screen plate. At the bottom of the screen plate, there are a plurality of narrow access slots that provide access to the steam discharge chambers, respectively. The access slots are covered by a removable cleanout bar. Since the access slots are narrow and located at the bottom of the screen, the steam shower of the Passiniemi publication appears to provide only limited access to the steam diffusers.
A steam shower that provides access to both steam diffusers and steam valve modules is shown in European patent application EP1310591A2 to Wegehaupt. The steam shower in EP1310591A2 has an interior box telescopically mounted inside an exterior box. The interior box includes all of the working components of the steam shower, including a main steam header, steam diffusers and steam valve modules. The interior box may be slid longitudinally outward to provide access to the steam diffusers and the steam valves. While the steam shower of EP1310591A2 provides access to both the steam diffusers and the steam valve modules, the steam shower requires the main steam header to be moved along with the steam diffusers and the steam valve modules, which unnecessarily increases the weight of the components that have be moved to provide the access.
Based on the foregoing, there is a need in the art for a steam shower that provides improved access to its steam diffusers and/or its steam valve modules. The present invention is directed to such a steam shower.